Response Reactions:  A Mathematical Well-Defined Way to Obtain Accurate Thermochemistry from ab Initio Calculations

The concept of stoichiometrically unique reactions referred to as response reactions (RERs), earlier deduced by us in applications of chemical thermodynamics and kinetics, is extended to isodesmic reactions. Namely, it is shown that the additional stoichiometric constraints according to which the number and type of chemical bonds in a multiple chemical reaction system are conserved may be formally appended to the conventional RERs formalism. As a result, one can define and generate a stoichiometrically unique class of isodesmic RERs. Along with the conventional RERs, the newly defined isodesmic RERs are shown to be effective in converting the total enthalpies of the species obtained from ab initio calculations into accurate values of the standard enthalpies of formations for large species.